Although the existence of syndiotactic polypropylenes has been known from old days, those produced by the conventional process, in which propylene is polymerized at a low temperature in the presence of a catalyst comprising a vanadium compound, an ether and an organoaluminum, are of low syndiotacticity and hence can hardly be regarded as characterizing syndiotactic polypropylenes. On the other hand, a polypropylene of a good tacticity, e.g., a syndiotactic pentad fraction of more than 0.7, has been discovered for the first time by J. A. Ewen et al. by the use of a catalyst comprising a transition metal compound having an asymmetric ligand and an aluminoxane (J. Am. Chem. Soc., 1988, 110, 6255-6256).
The above-mentioned method by J. A. Ewen et al. exhibits a good activity per unit amount of the transition metal and gives the resultant polypropylene a high tacticity and fairly excellent properties. However, the surface of its molded articles is so sticky that it has raised problems on practical use.